Fluids & Electrolytes: Mechanisms & Dehydration

istribution of Body Water – TBW, ICF and ECF

𝗧𝗼𝘁𝗮𝗹 𝗕𝗼𝗱𝘆 𝗪𝗮𝘁𝗲𝗿 (𝗧𝗕𝗪): All the water in the body, divided into intracellular and extracellular compartments. 𝗜𝗻𝘁𝗿𝗮𝗰𝗲𝗹𝗹𝘂𝗹𝗮𝗿 𝗙𝗹𝘂𝗶𝗱 (𝗜𝗖𝗙): Inside cells; approximately two-thirds of TBW in the usual adult model. 𝗘𝘅𝘁𝗿𝗮𝗰𝗲𝗹𝗹𝘂𝗹𝗮𝗿 𝗙𝗹𝘂𝗶𝗱 (𝗘𝗖𝗙): Outside cells; approximately one-third of TBW, divided into intravascular, interstitial and transcellular fluid. 𝗜𝗻𝘁𝗿𝗮𝘃𝗮𝘀𝗰𝘂𝗹𝗮𝗿 𝗙𝗹𝘂𝗶𝗱: Plasma within blood vessels; maintains circulating volume and tissue perfusion. 𝗜𝗻𝘁𝗲𝗿𝘀𝘁𝗶𝘁𝗶𝗮𝗹 𝗙𝗹𝘂𝗶𝗱: Between and around cells; enables exchange with capillaries. 𝗧𝗿𝗮𝗻𝘀𝗰𝗲𝗹𝗹𝘂𝗹𝗮𝗿 𝗙𝗹𝘂𝗶𝗱: Specialized spaces, including CSF, GI fluids, pericardial and peritoneal fluid.

Movement of Fluids – Osmosis, Diffusion, Active Transport and Filtration

𝗢𝘀𝗺𝗼𝘀𝗶𝘀: Water crosses a selectively permeable membrane toward the side with higher effective solute concentration (higher tonicity). 𝗗𝗶𝗳𝗳𝘂𝘀𝗶𝗼𝗻: Particles move from higher to lower concentration, down their gradient. 𝗔𝗰𝘁𝗶𝘃𝗲 𝗧𝗿𝗮𝗻𝘀𝗽𝗼𝗿𝘁: Substances move against their gradient using energy (ATP), such as the Na⁺/K⁺ pump. 𝗙𝗶𝗹𝘁𝗿𝗮𝘁𝗶𝗼𝗻: Water and small solutes move across a membrane because of a pressure difference. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: Higher sodium outside a cell draws water out by osmosis → the cell shrinks.

Hydrostatic Pressure vs Oncotic Pressure

𝗛𝘆𝗱𝗿𝗼𝘀𝘁𝗮𝘁𝗶𝗰 𝗣𝗿𝗲𝘀𝘀𝘂𝗿𝗲: Pressure exerted by blood on capillary walls, tending to push water out into interstitial tissue. 𝗢𝗻𝗰𝗼𝘁𝗶𝗰 𝗣𝗿𝗲𝘀𝘀𝘂𝗿𝗲: Osmotic pull produced mainly by plasma proteins (especially albumin), tending to retain water in the blood vessels. 𝗞𝗲𝘆 𝗗𝗶𝗳𝗳𝗲𝗿𝗲𝗻𝗰𝗲: Hydrostatic = outward push. Oncotic = inward/retaining pull. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗟𝗶𝗻𝗸: An imbalance can produce edema or reduce effective circulating blood volume.

ADH vs Aldosterone – Response to Dehydration

𝗧𝗿𝗶𝗴𝗴𝗲𝗿: Decreased blood volume/pressure or increased plasma osmolality activates fluid-conserving mechanisms. 𝗔𝗗𝗛: Made in hypothalamus, released by posterior pituitary; increases kidney water reabsorption → less, more concentrated urine. 𝗔𝗹𝗱𝗼𝘀𝘁𝗲𝗿𝗼𝗻𝗲: Produced by adrenal cortex, stimulated mainly by RAAS; increases renal Na⁺ reabsorption → water follows; promotes K⁺ excretion. 𝗥𝗔𝗔𝗦: Reduced renal perfusion → renin → angiotensin II (vasoconstriction) → aldosterone release. 𝗞𝗲𝘆 𝗗𝗶𝘀𝘁𝗶𝗻𝗰𝘁𝗶𝗼𝗻: ADH conserves WATER; aldosterone primarily conserves SODIUM (and therefore water).

Infants – Total Body Water and High Dehydration Risk

𝗧𝗼𝘁𝗮𝗹 𝗕𝗼𝗱𝘆 𝗪𝗮𝘁𝗲𝗿: Infants have approximately 70–80% of body weight as water (lecture: about 75%), versus approximately 45% in adolescents. 𝗪𝗵𝘆 𝗛𝗶𝗴𝗵 𝗥𝗶𝘀𝗸: Large surface area relative to weight → greater insensible loss; high metabolic rate → greater requirements; high ECF proportion → rapid fluid turnover. 𝗜𝗺𝗺𝗮𝘁𝘂𝗿𝗲 𝗞𝗶𝗱𝗻𝗲𝘆𝘀: Limited ability to concentrate urine and conserve water during poor intake. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗖𝗼𝗻𝘀𝗲𝗾𝘂𝗲𝗻𝗰𝗲: Fever, vomiting, diarrhea or poor feeding can cause rapid dehydration, especially in young infants.

Infant Fluid Imbalance – Mechanism and Clinical Assessment

𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: A relatively large ECF compartment loses fluid quickly with diarrhea/vomiting → reduced ECF and potentially intravascular volume and perfusion. 𝗞𝗶𝗱𝗻𝗲𝘆 𝗟𝗶𝗺𝗶𝘁𝗮𝘁𝗶𝗼𝗻: Immature kidneys cannot concentrate urine as efficiently, even when ADH rises → reduced ability to conserve water. 𝗔𝘀𝘀𝗲𝘀𝘀𝗺𝗲𝗻𝘁: Monitor weight changes, intake/output, urine, heart rate, mucous membranes, tears, fontanelle, skin turgor, capillary refill and alertness. 𝗘𝘅𝗰𝗲𝘀𝘀 𝗙𝗿𝗲𝗲 𝗪𝗮𝘁𝗲𝗿: Can dilute serum Na⁺ → hyponatremia, cerebral edema and seizures. Under 6 months, breast milk/formula normally supplies required fluids. 𝗘𝗮𝗿𝗹𝘆 𝗪𝗮𝗿𝗻𝗶𝗻𝗴: Reduced urine, increasing thirst/irritability, dry mouth and tachycardia; hypotension is a late danger sign.

Dehydration vs Hypovolemia

𝗗𝗲𝗵𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻: A deficit in total body water because fluid losses exceed intake (often accompanied by electrolyte losses). 𝗛𝘆𝗽𝗼𝘃𝗼𝗹𝗲𝗺𝗶𝗮: Reduction in effective circulating intravascular volume, compromising venous return and tissue perfusion. 𝗥𝗲𝗹𝗮𝘁𝗶𝗼𝗻𝘀𝗵𝗶𝗽: GI fluid loss often begins in the ECF; worsening loss may deplete intravascular volume → tachycardia, poor perfusion and shock. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁: Not every water deficit initially causes shock, but significant hypovolemia can cause life-threatening circulatory failure.

Compensation for Dehydration – Infants/Children vs Adults

𝗔𝗱𝘂𝗹𝘁 𝗥𝗲𝘀𝗽𝗼𝗻𝘀𝗲: ADH and RAAS conserve fluid; tachycardia and peripheral vasoconstriction help divert blood from skin/GI tissues to heart and brain. 𝗖𝗵𝗶𝗹𝗱 𝗥𝗲𝘀𝗽𝗼𝗻𝘀𝗲: Children also vasoconstrict and increase heart rate, so BP may remain normal despite significant volume loss. 𝗪𝗵𝘆 𝗖𝗵𝗶𝗹𝗱𝗿𝗲𝗻 𝗗𝗲𝘁𝗲𝗿𝗶𝗼𝗿𝗮𝘁𝗲 𝗙𝗮𝘀𝘁𝗲𝗿: Smaller fluid reserves, greater relative fluid needs and (especially in infants) poorer renal concentrating capacity. 𝗘𝘅𝗮𝗺 𝗪𝗮𝗿𝗻𝗶𝗻𝗴: Hypotension is a LATE sign of pediatric shock. Look earlier for tachycardia, cool extremities, weak pulses, prolonged capillary refill and oliguria.

Normal Urine Output – Infants

𝗘𝘅𝗽𝗲𝗰𝘁𝗲𝗱 𝗢𝘂𝘁𝗽𝘂𝘁: About 1–2 mL/kg/hour in infants; the lecture uses approximately 2 mL/kg/hour as the average. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: A 6 kg infant producing 2 mL/kg/hour should make about 12 mL urine/hour. 𝗪𝗵𝘆 𝗜𝘁 𝗠𝗮𝘁𝘁𝗲𝗿𝘀: Falling output suggests dehydration, reduced renal perfusion or kidney dysfunction; interpret with age and clinical condition. 𝗡𝘂𝗿𝘀𝗶𝗻𝗴 𝗖𝗮𝗿𝗲: Track wet diapers and accurate intake/output where possible.

Normal Urine Output – Older Children

𝗘𝘅𝗽𝗲𝗰𝘁𝗲𝗱 𝗢𝘂𝘁𝗽𝘂𝘁: Approximately 0.5–1 mL/kg/hour in older children (the lesson's range); at least 1 mL/kg/hour is often used as a target in younger children. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: A 20 kg child at 1 mL/kg/hour makes 20 mL/hour; at 0.5 mL/kg/hour makes 10 mL/hour. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝗰𝗲: A sustained fall from age-appropriate urine output raises concern for dehydration, reduced kidney perfusion or renal impairment.

Hypovolemic Shock – Mechanism and Clinical Signs

𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: Severe loss of ECF/intravascular volume → reduced venous return/preload → lower stroke volume and cardiac output → impaired oxygen delivery and organ perfusion. 𝗘𝗮𝗿𝗹𝘆 𝗖𝗼𝗺𝗽𝗲𝗻𝘀𝗮𝘁𝗶𝗼𝗻: Tachycardia and peripheral vasoconstriction; BP can initially remain normal. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗦𝗶𝗴𝗻𝘀: Weak/thready pulses, cold or mottled extremities, prolonged capillary refill, oliguria, irritability progressing to lethargy and altered consciousness. 𝗔𝘀𝘀𝗼𝗰𝗶𝗮𝘁𝗲𝗱 𝗗𝗲𝗵𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻 𝗦𝗶𝗴𝗻𝘀: Very dry/parched mouth, absent tears, sunken eyes/fontanelle and poor skin turgor. 𝗟𝗮𝘁𝗲 𝗖𝗿𝗶𝘁𝗶𝗰𝗮𝗹 𝗦𝗶𝗴𝗻: Hypotension/shock = urgent circulatory failure requiring immediate intervention.

Conditions That INCREASE Fluid Requirements

𝗙𝗲𝘃𝗲𝗿: Lecture estimates approximately 12% more fluid requirement for each 1°C rise in body temperature, due to insensible losses. 𝗚𝗜 𝗟𝗼𝘀𝘀𝗲𝘀: Vomiting and diarrhea directly remove water and electrolytes. 𝗥𝗲𝘀𝗽𝗶𝗿𝗮𝘁𝗼𝗿𝘆 𝗟𝗼𝘀𝘀𝗲𝘀: Tachypnea increases evaporative loss. 𝗢𝘁𝗵𝗲𝗿 𝗖𝗼𝗻𝗱𝗶𝘁𝗶𝗼𝗻𝘀: Burns, major losses associated with shock, phototherapy and radiant warmers in infants. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗣𝗼𝗶𝗻𝘁: Add measured ongoing losses to baseline needs and adjust to the child's condition.

Conditions That DECREASE Fluid Requirements

𝗖𝗮𝗿𝗱𝗶𝗮𝗰 𝗙𝗮𝗶𝗹𝘂𝗿𝗲: Reduced ability to tolerate extra volume; risk of fluid overload. 𝗢𝗹𝗶𝗴𝘂𝗿𝗶𝗰 𝗥𝗲𝗻𝗮𝗹 𝗙𝗮𝗶𝗹𝘂𝗿𝗲: Reduced urine excretion → fluid retention. 𝗦𝗜𝗔𝗗𝗛: Excess ADH retains free water and may cause dilutional hyponatremia. 𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝗰𝗮𝗹 𝗩𝗲𝗻𝘁𝗶𝗹𝗮𝘁𝗶𝗼𝗻: Humidified ventilation may reduce insensible respiratory loss. 𝗡𝘂𝗿𝘀𝗶𝗻𝗴 𝗣𝗼𝗶𝗻𝘁: Maintenance formulas are estimates; prescribed volume may need restriction and close monitoring.

Isotonic Dehydration – ECF Loss

𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: Water and Na⁺ are lost in approximately equal proportions → serum Na⁺ remains 135–145 mEq/L; this is a common pediatric dehydration type. 𝗖𝗼𝗺𝗽𝗮𝗿𝘁𝗺𝗲𝗻𝘁 𝗘𝗳𝗳𝗲𝗰𝘁: Fluid is lost mainly from the ECF (interstitial and intravascular spaces); ECF tonicity changes little → no major osmotic shift into or out of cells, which stay near normal size. 𝗖𝗮𝘂𝘀𝗲𝘀: Gastroenteritis with vomiting/diarrhea and other near-isotonic losses; hemorrhage similarly produces isotonic volume loss/hypovolemia. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗦𝗶𝗴𝗻𝘀: Thirst, reduced urine, tachycardia, dry mucosa and diminished perfusion as losses progress. 𝗠𝗮𝗷𝗼𝗿 𝗗𝗮𝗻𝗴𝗲𝗿: Hypovolemic shock from ECF/intravascular volume depletion.

Hypotonic Dehydration and Hyponatremia – Cell Swelling

𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: More sodium than water is lost → serum Na⁺ below 135 mEq/L and reduced ECF tonicity. 𝗙𝗹𝘂𝗶𝗱 𝗦𝗵𝗶𝗳𝘁: The ECF becomes relatively dilute → water shifts FROM ECF INTO ICF → cells swell, including brain cells. 𝗖𝗶𝗿𝗰𝘂𝗹𝗮𝘁𝗼𝗿𝘆 𝗘𝗳𝗳𝗲𝗰𝘁: Already-depleted ECF loses further water to cells → greater risk of early/severe hypovolemia and shock. 𝗦𝗶𝗴𝗻𝘀: Dehydration findings plus headache, lethargy, altered behavior or seizures from cerebral swelling. 𝗖𝗮𝘂𝘀𝗲𝘀: Diarrhea replaced with plain water/hypotonic drinks; salt-wasting conditions (e.g., congenital adrenal hyperplasia, cystic fibrosis) or diuretics.

Hypertonic Dehydration and Hypernatremia – Cell Shrinkage

𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: More water than sodium is lost → serum Na⁺ above 145 mEq/L and increased ECF tonicity. 𝗙𝗹𝘂𝗶𝗱 𝗦𝗵𝗶𝗳𝘁: Concentrated ECF draws water FROM ICF INTO ECF → cells, including brain cells, shrink. 𝗖𝗶𝗿𝗰𝘂𝗹𝗮𝘁𝗼𝗿𝘆 𝗘𝗳𝗳𝗲𝗰𝘁: ICF-to-ECF shift partly maintains circulation; shock may appear later despite major total water loss. 𝗦𝗶𝗴𝗻𝘀: Thirst, irritability, lethargy, neurological abnormalities or seizures; skin may feel doughy. 𝗖𝗮𝘂𝘀𝗲𝘀: Fever/diarrhea with inadequate water intake, overly concentrated infant formula and diabetes insipidus. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁 𝗥𝗶𝘀𝗸: Overly rapid correction can shift water into brain cells → cerebral edema.

Normal Serum Sodium – Range and Role

𝗡𝗼𝗿𝗺𝗮𝗹 𝗩𝗮𝗹𝘂𝗲: 135–145 mEq/L (for sodium, numerically equal to mmol/L). 𝗥𝗼𝗹𝗲: Na⁺ is the main extracellular cation and a key determinant of ECF tonicity and water distribution. 𝗟𝗼𝘄 𝗦𝗼𝗱𝗶𝘂𝗺: Hyponatremia below 135 → water tends to enter cells (swelling). 𝗛𝗶𝗴𝗵 𝗦𝗼𝗱𝗶𝘂𝗺: Hypernatremia above 145 → water tends to leave cells (shrinkage).

Mild Dehydration – Weight Loss and Clinical Signs

𝗪𝗲𝗶𝗴𝗵𝘁 𝗟𝗼𝘀𝘀: Infants: about 3–5% of previous body weight. Older children: about 3–4%. 𝗩𝗶𝘁𝗮𝗹 𝗦𝗶𝗴𝗻𝘀: Pulse, respiratory rate and BP generally normal; capillary refill usually 2 seconds or less. 𝗔𝗽𝗽𝗲𝗮𝗿𝗮𝗻𝗰𝗲: Normal alert behavior, slight thirst, moist mucous membranes, tears still present, normal fontanelle and skin turgor. 𝗨𝗿𝗶𝗻𝗲/𝗩𝗲𝗶𝗻𝘀: Urine may be somewhat reduced; external jugular vein visible when supine. 𝗔𝘀𝘀𝗲𝘀𝘀𝗺𝗲𝗻𝘁: Compare current with pre-illness weight and monitor progression.

Moderate Dehydration – Weight Loss and Clinical Signs

𝗪𝗲𝗶𝗴𝗵𝘁 𝗟𝗼𝘀𝘀: Infants: about 6–9%. Older children: about 6–8%. 𝗩𝗶𝘁𝗮𝗹 𝗦𝗶𝗴𝗻𝘀: Slight tachycardia/tachypnea; BP may remain normal or show orthostatic change. 𝗔𝗽𝗽𝗲𝗮𝗿𝗮𝗻𝗰𝗲: Irritable, increased thirst, dry mucous membranes, decreased tears, anterior fontanelle may become sunken. 𝗦𝗸𝗶𝗻/𝗣𝗲𝗿𝗳𝘂𝘀𝗶𝗼𝗻: Reduced skin turgor; delayed capillary refill about 2–4 seconds. 𝗨𝗿𝗶𝗻𝗲/𝗩𝗲𝗶𝗻𝘀: Oliguria; external jugular vein less visible (may require supraclavicular pressure). 𝗧𝗿𝗲𝗮𝘁𝗺𝗲𝗻𝘁 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲: ORT if alert, adequately perfused and able to tolerate it.

Severe Dehydration – Weight Loss and Clinical Signs

𝗪𝗲𝗶𝗴𝗵𝘁 𝗟𝗼𝘀𝘀: Infants: approximately 10% or more. Older children: approximately 10% or more. 𝗩𝗶𝘁𝗮𝗹 𝗦𝗶𝗴𝗻𝘀: Marked tachycardia; deep/rapid breathing; orthostatic hypotension progressing to shock. 𝗕𝗲𝗵𝗮𝘃𝗶𝗼𝗿: Marked irritability progressing to lethargy, severe thirst or reduced responsiveness. 𝗠𝗼𝘂𝘁𝗵/𝗘𝘆𝗲𝘀: Parched mucosa, no tears, sunken eyes and sunken anterior fontanelle. 𝗦𝗸𝗶𝗻/𝗣𝗲𝗿𝗳𝘂𝘀𝗶𝗼𝗻: Capillary refill longer than 4 seconds, marked tenting, cool/cyanotic/mottled extremities; jugular vein not visible. 𝗨𝗿𝗶𝗻𝗲: Marked oliguria or anuria. 𝗘𝗺𝗲𝗿𝗴𝗲𝗻𝗰𝘆 𝗖𝗹𝘂𝗲: Sleepy child + weak pulses + cold extremities + 4-second refill → assess urgently for shock.

Isotonic IV Fluids – Examples, Mechanism and Use

𝗘𝘅𝗮𝗺𝗽𝗹𝗲𝘀: 0.9% NaCl (normal saline), Lactated Ringer's and Ringer's solution. 𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: Near-plasma effective tonicity → expands ECF, including circulating blood volume, without a major shift of water into/out of cells. 𝗨𝘀𝗲: Initial volume replacement and shock resuscitation as indicated. 𝗗𝟱𝗪 𝗡𝘂𝗮𝗻𝗰𝗲: The slide lists 5% dextrose in water as isotonic by initial osmolarity, but after glucose metabolism D5W acts like free water (physiologically hypotonic); NEVER use D5W alone for a shock bolus.

Hypotonic IV Fluids – Examples and Mechanism

𝗘𝘅𝗮𝗺𝗽𝗹𝗲𝘀: 0.45%, 0.33% and 0.2% NaCl (lecture examples); 2.5% dextrose water is also listed. 𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: Lower effective tonicity than plasma → relatively more free water; water shifts from ECF INTO cells by osmosis. 𝗘𝗳𝗳𝗲𝗰𝘁: Can increase intracellular hydration but lower serum Na⁺ and promote cellular swelling. 𝗦𝗮𝗳𝗲𝘁𝘆: Not appropriate as an initial shock-resuscitation bolus; hypotonic therapy requires close sodium/neurological monitoring and a specific indication.

Hypertonic IV Fluids – Examples and Mechanism

𝗘𝘅𝗮𝗺𝗽𝗹𝗲𝘀: 3% or 5% NaCl (lecture examples). 𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺: Higher tonicity than plasma → draws water OUT of cells INTO ECF; raises extracellular sodium concentration. 𝗘𝗳𝗳𝗲𝗰𝘁: Expands ECF and decreases cellular swelling. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗨𝘀𝗲: 3% saline may be used for severe symptomatic hyponatremia under an emergency protocol. 𝗦𝗮𝗳𝗲𝘁𝘆: Rapid sodium changes can cause serious neurological harm; require protocol-directed dosing and monitoring.

IV Maintenance Fluids – Purpose and 100–50–20 Rule

𝗣𝘂𝗿𝗽𝗼𝘀𝗲: Provide baseline daily water needs when a child cannot meet intake orally, e.g., fasting before surgery, procedural sedation or other NPO periods. 𝗠𝗲𝘁𝗵𝗼𝗱: Holliday–Segar 100–50–20 calculates estimated mL per 24 hours: first 10 kg at 100 mL/kg; next 10 kg at 50 mL/kg; every kg over 20 at 20 mL/kg. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁 𝗗𝗶𝘀𝘁𝗶𝗻𝗰𝘁𝗶𝗼𝗻: MAINTENANCE covers normal daily needs; it does not by itself replace an existing dehydration DEFICIT or ongoing abnormal losses. 𝗣𝗿𝗮𝗰𝘁𝗶𝗰𝗲: Divide daily total by 24 for an hourly rate; adjust for clinical status. The slide table is not for neonates.

IV Maintenance – The 100 Rule (1–10 kg)

𝗥𝘂𝗹𝗲: For body weight 1–10 kg: 100 mL/kg/DAY. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 5 kg child × 100 mL/kg/day = 500 mL/day. 𝗛𝗼𝘂𝗿𝗹𝘆 𝗥𝗮𝘁𝗲: 500 ÷ 24 = 20.8, approximately 21 mL/hour. 𝗞𝗲𝘆 𝗣𝗼𝗶𝗻𝘁: The 100 is mL/kg/DAY, not mL/kg/hour.

IV Maintenance – The 50 Rule (11–20 kg)

𝗥𝘂𝗹𝗲: First 10 kg = 1,000 mL/day; add 50 mL/kg/day for EACH kg above 10. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 15 kg child = 1,000 + (5 × 50) = 1,250 mL/day. 𝗛𝗼𝘂𝗿𝗹𝘆 𝗥𝗮𝘁𝗲: 1,250 ÷ 24 = 52.1, approximately 52 mL/hour. 𝗞𝗲𝘆 𝗣𝗼𝗶𝗻𝘁: Do not multiply all 15 kg by 50; only the 5 kg over 10 use the 50 rate.

IV Maintenance – The 20 Rule (Over 20 kg)

𝗥𝘂𝗹𝗲: First 20 kg = 1,500 mL/day; add 20 mL/kg/day for EACH kg above 20. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 25 kg child = 1,500 + (5 × 20) = 1,600 mL/day. 𝗛𝗼𝘂𝗿𝗹𝘆 𝗥𝗮𝘁𝗲: 1,600 ÷ 24 = 66.7, approximately 67 mL/hour. 𝗔𝗱𝗱𝗶𝘁𝗶𝗼𝗻𝗮𝗹 𝗘𝘅𝗮𝗺 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 35 kg = 1,500 + (15 × 20) = 1,800 mL/day = 75 mL/hour.

Oral Rehydration Therapy (ORT) – Indications, Solution and Goals

𝗜𝗻𝗱𝗶𝗰𝗮𝘁𝗶𝗼𝗻𝘀: Preferred for mild/moderate dehydration in a child who is alert, responsive, adequately perfused and able to tolerate enteral fluids; not for established shock. 𝗦𝗼𝗹𝘂𝘁𝗶𝗼𝗻: ORS contains balanced sodium/electrolytes plus glucose; intestinal glucose–sodium cotransport promotes sodium absorption and water follows by osmosis. 𝗧𝗵𝗿𝗲𝗲 𝗚𝗼𝗮𝗹𝘀: Correct existing deficit over approximately 4–6 hours; replace ongoing vomiting/diarrhea losses; provide normal maintenance needs. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁: Use ORS rather than plain water or sugary drinks when replacing dehydration-related electrolyte losses.

ORS in a Vomiting Child

𝗠𝗲𝘁𝗵𝗼𝗱: Give 2–5 mL ORS every 2–3 minutes using a syringe, spoon or medicine cup; increase gradually as tolerated. 𝗥𝗮𝘁𝗶𝗼𝗻𝗮𝗹𝗲: Small frequent amounts are less likely to provoke further vomiting than large drinks. 𝗠𝗲𝗱𝗶𝗰𝗮𝘁𝗶𝗼𝗻: Ondansetron (Zofran) may be used when clinically indicated in acute gastroenteritis to reduce vomiting and support successful ORT. 𝗥𝗲𝗮𝘀𝘀𝗲𝘀𝘀: Monitor alertness, hydration/perfusion, urine and ability to tolerate fluids; persistent failure or severe illness may require IV therapy.

ORS Dose by Dehydration Severity and Ongoing Diarrhea

𝗠𝗶𝗹𝗱 𝗗𝗲𝗵𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻: 50 mL/kg ORS during the initial rehydration period (lecture example: about 4 hours). 𝗠𝗼𝗱𝗲𝗿𝗮𝘁𝗲 𝗗𝗲𝗵𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻: 100 mL/kg ORS over the initial period. 𝗢𝗻𝗴𝗼𝗶𝗻𝗴 𝗗𝗶𝗮𝗿𝗿𝗵𝗲𝗮: Add 10 mL/kg ORS for EACH new watery stool, in addition to the initial rehydration volume. 𝗙𝗼𝗿𝗺𝘂𝗹𝗮: Total ORS = initial (weight × severity dose) + (number of new stools × weight × 10 mL/kg). 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗣𝗼𝗶𝗻𝘁: Give in divided portions; reassess ongoing losses and response.

Clinical ORS Calculation – 12 kg, Moderate Dehydration, Two Stools

𝗖𝗮𝘀𝗲: A 12 kg child has moderate dehydration and then has 2 additional watery stools during rehydration. 𝗜𝗻𝗶𝘁𝗶𝗮𝗹 𝗢𝗥𝗦: 12 kg × 100 mL/kg = 1,200 mL (initial 4-hour course). 𝗢𝗻𝗴𝗼𝗶𝗻𝗴 𝗦𝘁𝗼𝗼𝗹 𝗟𝗼𝘀𝘀𝗲𝘀: 10 mL/kg/stool × 12 kg = 120 mL per new stool; 2 stools × 120 mL = 240 mL extra. 𝗧𝗼𝘁𝗮𝗹 𝗢𝗥𝗦: 1,200 + 240 = 1,440 mL (given gradually and adjusted to tolerance). 𝗘𝘅𝗮𝗺 𝗧𝗿𝗮𝗽: For 12 kg, each stool is 120 mL extra, NOT 100 mL; total is NOT 1,400 mL.

IV Therapy for Dehydration – Indications and Stages

𝗪𝗵𝗲𝗻 𝗜𝗩 𝗜𝘀 𝗜𝗻𝗱𝗶𝗰𝗮𝘁𝗲𝗱: Severe dehydration, shock, altered consciousness, inability to drink safely or ORT failure from persistent vomiting. 𝗙𝗹𝘂𝗶𝗱 𝗖𝗵𝗼𝗶𝗰𝗲: Use isotonic crystalloid (0.9% NaCl or Lactated Ringer's) for initial resuscitation, NOT dextrose-only solution. 𝗦𝘁𝗮𝗴𝗲 𝟭 – 𝗥𝗲𝘀𝘂𝘀𝗰𝗶𝘁𝗮𝘁𝗶𝗼𝗻: If shock, rapid isotonic bolus (lecture: 20 mL/kg over about 5–20 min), then reassess perfusion. 𝗦𝘁𝗮𝗴𝗲 𝟮 – 𝗥𝗲𝗽𝗹𝗮𝗰𝗲𝗺𝗲𝗻𝘁: Correct remaining fluid deficit and ongoing losses, with electrolyte/kidney monitoring. 𝗦𝘁𝗮𝗴𝗲 𝟯 – 𝗠𝗮𝗶𝗻𝘁𝗲𝗻𝗮𝗻𝗰𝗲/𝗥𝗲𝗰𝗼𝘃𝗲𝗿𝘆: Meet daily needs and resume oral feeding/fluids as stable. 𝗠𝗼𝗻𝗶𝘁𝗼𝗿: Cardiorespiratory status, pulses, capillary refill, urine output and signs of overload.

Fluid Deficit – Definition and Calculation

𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻: Fluid already LOST during illness (e.g., diarrhea/vomiting), separate from ongoing daily maintenance requirements. 𝗪𝗲𝗶𝗴𝗵𝘁 𝗠𝗲𝘁𝗵𝗼𝗱: Fluid deficit (mL) ≈ [pre-illness weight (kg) − current weight (kg)] × 1,000 mL/kg. 𝗪𝗵𝘆: An acute loss of 1 kg body weight is approximately 1 L (1,000 mL) of fluid. 𝗣𝗲𝗿𝗰𝗲𝗻𝘁 𝗗𝗲𝗵𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻: (Weight lost ÷ pre-illness weight) × 100. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 11.000 − 10.540 = 0.460 kg lost ≈ 460 mL deficit; 0.460 ÷ 11 × 100 = 4.18%. 𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁: 1,000 mL per kg of LOST weight is a conversion, NOT the IV maintenance prescription.

Shock Bolus – Purpose, Fluid and Calculation

𝗣𝘂𝗿𝗽𝗼𝘀𝗲: Rapidly restore circulating ECF/intravascular volume and tissue perfusion in hypovolemic shock. 𝗙𝗹𝘂𝗶𝗱: Isotonic crystalloid, such as 0.9% NaCl or Lactated Ringer's; do not give dextrose-only fluid as resuscitation bolus. 𝗟𝗲𝗰𝘁𝘂𝗿𝗲 𝗗𝗼𝘀𝗲: 20 mL/kg IV, commonly over 5–20 minutes in the slide protocol, with prompt reassessment. 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 10 kg × 20 mL/kg = 200 mL bolus. 𝗥𝗲𝗮𝘀𝘀𝗲𝘀𝘀: Heart rate, pulses, capillary refill, BP, mentation, work of breathing and urine output; modify for cardiac/renal disease or local protocol. 𝗞𝗲𝘆 𝗗𝗶𝘀𝘁𝗶𝗻𝗰𝘁𝗶𝗼𝗻: A shock bolus is RAPID resuscitation, not the 24-hour maintenance/deficit infusion.

Clinical Case – 18-Month-Old: Maintenance, Deficit and Shock Bolus

𝗖𝗮𝘀𝗲: 18-month-old girl: previous weight 11 kg, now 10.540 kg; 7 watery stools, 4 vomits, reduced urine, dry mucosa; alert and perfused; oral ORS not tolerated; Na⁺ 139 mmol/L. 𝗔𝘀𝘀𝗲𝘀𝘀𝗺𝗲𝗻𝘁: Weight lost = 0.460 kg; (0.460 ÷ 11) × 100 = 4.18% = MILD dehydration; sodium normal = ISOTONIC. IV rehydration may be used because ORT failed, but no shock bolus is initially required with adequate perfusion. 𝗠𝗮𝗶𝗻𝘁𝗲𝗻𝗮𝗻𝗰𝗲: Use pre-illness weight 11 kg: 1,000 mL (first 10 kg) + 1 × 50 mL = 1,050 mL/day. 𝗗𝗲𝗳𝗶𝗰𝗶𝘁: 11 − 10.540 = 0.460 kg lost ≈ 460 mL to replace. 𝗧𝗼𝘁𝗮𝗹 𝗙𝗼𝗿 𝟮𝟰 𝗛𝗼𝘂𝗿𝘀 – 𝗟𝗲𝗰𝘁𝘂𝗿𝗲 𝗘𝘅𝗮𝗺𝗽𝗹𝗲: 1,050 + 460 = 1,510 mL/24 h; 1,510 ÷ 24 = 62.9 ≈ 63 mL/hour. Add ongoing losses separately and subtract fluid already given. 𝗜𝗳 𝗛𝘆𝗽𝗼𝘃𝗼𝗹𝗲𝗺𝗶𝗰 𝗦𝗵𝗼𝗰𝗸 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝘀: New lethargy + cold extremities + weak pulses + delayed refill → urgent isotonic bolus: 20 mL/kg × CURRENT 10.540 kg = 210.8 ≈ 211 mL, then immediate reassessment. Recalculate subsequent fluids after any bolus. 𝗠𝗼𝗻𝗶𝘁𝗼𝗿: Perfusion, vitals, weight, urine output, Na⁺/glucose, respiratory status and overload. This 24-hour calculation is the lecturer's simplified stable-child example, not a universal prescription.

Clinical Indicators of Successful Rehydration

𝗛𝘆𝗱𝗿𝗮𝘁𝗶𝗼𝗻 𝗦𝗶𝗴𝗻𝘀: Moist mucous membranes; restored tears/skin turgor; improving thirst and mental status. 𝗣𝗲𝗿𝗳𝘂𝘀𝗶𝗼𝗻: Heart rate normalizing, warm extremities and capillary refill about 2 seconds or less. 𝗨𝗿𝗶𝗻𝗲 𝗢𝘂𝘁𝗽𝘂𝘁: Returning to age-appropriate levels (often at least 1 mL/kg/hour in younger children). 𝗟𝗮𝗯𝗼𝗿𝗮𝘁𝗼𝗿𝘆: Improvement or normalization of Na⁺ and K⁺ abnormalities when present. 𝗡𝘂𝗿𝘀𝗶𝗻𝗴 𝗠𝗼𝗻𝗶𝘁𝗼𝗿𝗶𝗻𝗴: Intake/output, serial weights, vital signs, neurological status and signs of fluid overload. 𝗞𝗲𝘆 𝗣𝗼𝗶𝗻𝘁: Rehydration success requires both adequate hydration and adequate tissue perfusion